1. Field of the Invention
The invention relates to a process for the preparation of a conjugated polymer, in particular conjugated polymers suitable for use as an active material in organic semiconductor devices including optical devices such as electroluminescent or photovoltaic devices.
2. Description of Related Technology
Conjugated polyarylenes are widely used as the active material in organic semiconductor devices. Examples of such materials include polyfluorenes as disclosed in, for example, WO 99/54385, spirofluorenes as disclosed in, for example, EP 0707020, polyphenylenes as disclosed in, for example, G. Grem, G. Leditzky, B. Ullrich, G. Leising, Adv. Mater. (1992), 4, 36 and phenylene-thienylene copolymers as disclosed in, for example, K. Kaeriyama et al, Synth. Met. (2000), 111–112, 519–522.
Polyarylenes may suitably be prepared by Suzuki or Yamamoto polymerization. Of these two techniques, Suzuki polymerization is the only technique that enables exertion of control over the regioregularity of the copolymer. Thus Suzuki polymerization may be used to generate AB, block, or random copolymers depending on the relative quantities of boron and halo monomers used.
It is desirable for polyarylenes for use in the aforementioned optical devices to be of high molecular weight as this improves their processability. High viscosity is also advantageous for certain applications. However, a known drawback of Suzuki polymerization is the difficulty in reproducibly generating high molecular weight polymers. This has been attributed to the problem of side reactions competing with the polymerization, e.g. reductive elimination and deboronation of the monomers, which limit the molecular weight of the polymer. These side reactions are initially relatively insignificant but become prevalent at longer reaction times. A fast reaction rate is therefore desirable from the point of view of obtaining high molecular weight material.
U.S. Pat. No. 5,777,070 discloses the use of the phase transfer catalyst tricaprylylmethyl ammonium chloride in Suzuki polymerization reactions to facilitate the movement of the reactive boronate species between the organic and aqueous phases of the reaction mixture. In an alternative approach, GB 2360291 describes the use of tetraalkyl ammonium boronate salts soluble in the organic phase such that the polymerization reaction takes place in a single phase.